1. Technical Field
Various embodiments of the present disclosure relate to semiconductor light-emitting devices and, more particularly, to a method of separating nitride films from grow substrates by selective photo-enhanced wet oxidation.
2. Description of the Relevant Art
For high power blue light-emitting diodes (LEDs), III-nitride such as GaN (gallium nitride) or InGaN (indium gallium nitride) semiconductor material is typically grown on a sapphire substrate. For instance, a thin GaN film of a few microns thick is grown on a sapphire substrate. Major costs of LED fabrication are the sapphire substrate and the scribe-and-break operation. For the traditional LED configuration the sapphire is not removed. A vertical LED structure, however, requires removing the sapphire before attaching electrical contacts on the active epitaxy (epi) layer. Excimer lasers are typically utilized for separating the sapphire and GaN thin film in a technique known as laser lift-off.
Laser lift-off is a technique for detaching a sapphire substrate from III-nitride epi layers as used in the LED industry. Excimer lasers at 248 and 193 nm excel in this application as they provide large (several mm wide) spots on target with homogeneity better than +/−5%. The laser light goes through the back of a sapphire wafer causing photo-induced decomposition at the GaN/sapphire interface, and creates a localized explosive shock wave that debonds the interface. This technique can be used for wafer based LEDs as well as flip chips.
LED laser lift-off reduces the time and cost of the LED fabrication process, enabling the manufacturer to grow GaN LED film devices on the sapphire wafer, for example, prior to transfer the thin film device to a heat sink electrical interconnect. This process allows for the creation of free standing GaN films, and the integration of GaN LEDs onto virtually any carrier substrate.
However, as laser lift-off causes decomposition at the III-nitride epi layer/sapphire interface by way of a localized explosive shock wave that debonds the interface, quality of the III-nitride epi layer is inevitably impacted, degraded or otherwise compromised as a result of laser lift-off. In addition, laser lift-off tends to have issues such as yield rate, high costs of equipment, and environmental impact as a result of the use of high energy.
Techniques for separating the sapphire substrate from the III-nitride epi layer other than laser lift-off also exist, such wet etch and other techniques. Among these techniques, a technique for separating SiO/GaN nanocolumns and GaN film requires the use of HF to etch SiO nanocolumns to result in stress release. More specifically, GaN nanocolumns in epitaxial regrowth region are broken to allow separation of the GaN film and the substrate. At least in terms of industrial pollution and environmental protection, none of the aforementioned techniques is optimal.